International Mechanical Codes prescriptive and performance-related requirements establish minimal regulations for mechanical systems. The IMC was developed using broad-based concepts to accommodate new materials, technologies, and designs. Significant changes in the 2021 IMC include: International Mechanical Code

IMC 1st Edition Clothes dryer exhaust terminals must be at least 3 feet away from any building opening.
Spray-applied polyurethane foam on the exterior of ducts in attics and crawl spaces must meet specific smoke and flame index limitations.
Fire and smoke dampers now require authorized access for inspection and maintenance.
New refrigerants have been added to the refrigerant tables.
Condensate termination identification markers and discharge limitations have been introduced.
Manufacturer-approved combination intake/exhaust terminations are now permissible, easing separation requirements.
Minimum mechanical ventilation for whole-house balanced ventilation systems has been reduced by 30%.